1. Field of the Invention
The present invention relates to a circuit board, and more particularly, the present invention relates to a circuit board that reduces electromagnetic noise and interference.
2. Description of Related Art
The functions of electronic products are getting more complicated due to rapid development of technology. To increase the convenience for users, electronic products are also getting lighter, thinner, and smaller. To this end, the printed circuit board on which electronic elements are installed in electronic products is also made smaller, and the electronic elements are installed more closely to one another on the printed circuit board. Therefore, it becomes an even more important issue how each of  the electronic elements on the circuit board can be prevented from the electromagnetic noise and interference generated by themselves.
The electromagnetic noise and interference within a multi-layer printed circuit board mainly comes from high-speed digital signals or high-power elements, such as clock generators and power amplifiers. The noise can be transmitted as electromagnetic waves through the medium of a circuit board to the other elements on the printed circuit board. Since the distance between the metal power plane and the ground plane inside the multi-layer printed circuit board are almost the same, a parallel plate structure that transmits electromagnetic noise tends to be formed in the area sandwiched between the two metal layers.
To prevent the functioning of other elements from being affected by the electromagnetic noise, a method frequently adopted is to connect a decoupling capacitor near an IC. By using the low impedance of a decoupling capacitor at a high frequency, the electromagnetic noise of a high frequency can be effectively eliminated.
However, due to effective serial inductance of a capacitor, the decoupling capacitor cannot effectively filter out electromagnetic noise above 500 MHz.